1. Field of the Invention
This invention relates to a fuel injection pump whose prestroke is controlled by controlling the position of a control sleeve and to a prestroke controller therefor, more particularly to a fuel injection pump prestroke controller which enables prestroke to be controlled independently of one or more flyweights utilized for adjusting the fuel injection timing advance characteristic, and still more particularly to a fuel injection pump prestroke controller wherein displacement produced by the lift of one or more flyweights is transferred using a magnetic coupling.
2. Prior Art
A commonly employed type of fuel injection pump with adjustable prestroke varies the prestroke by controlling the position of a control sleeve fitted on the plunger of the fuel injection pump.
As this type of fuel injection pump is equipped with an electromagnetic prestroke actuator for controlling the position of the control sleeve, however, it is expensive to manufacture. Therefore, as taught in Japanese Patent Disclosure No. Hei 3-260339, for example, mechanical prestroke actuators were developed for reducing production cost. In the mechanical prestroke actuator, since the timing control rod is positionally controlled by the centrifugal force of one or more governor flyweights, it has to be extended into the interior of the governor housing for connecting it with the displacement transfer section of the governor.
However, since the interior of the main pump unit where the timing control rod is located is filled with fuel, while the interior of the governor housing is filled with engine oil, this arrangement is disadvantageous in that any fuel that leaks from the main pump unit will dilute the engine oil and degrade its lubrication performance.
Because of this, the practice has been to prevent fuel leakage by providing a fuel seal ring or an oil seal ring at the point where the timing control rod passes through the wall of the main pump unit.
This is not an altogether satisfactory solution, however, because fuel leakage is apt to occur anyway with increasing wear of the fuel seal ring or the oil seal ring and also because the increased resistance of the fuel seal ring or oil seal ring when the engine is cold, as when it is first started, degrades the displacement transfer performance.
Another drawback of the prior art configuration is that sticking of the control sleeve or timing control rod disables not only the control by the control sleeve but also the ability of the governor to control the fuel injection quantity.
In some prior art fuel injection pumps the fuel injection timing advance characteristic is adjusted by controlling the prestroke. In the fuel injection pump disclosed in Japanese Patent Disclosure No. Hei 3-233144, for example, the prestroke is adjusted and the fuel injection timing is controlled by utilizing the movement of the governor flyweight(s) as a source of driving power for operating the timing control rod.
In a fuel injection pump equipped with a plunger which sucks in and pressurizes fuel by reciprocating axially, the prestroke refers to the stroke of the plunger between its bottom dead point and the point at which pressurized fuel delivery starts. The fuel injection characteristic appropriate for the engine operating condition is obtained by shortening the prestroke to cause the fuel injection to start earlier (injection timing advance) or lengthening it to cause the fuel injection to start later (injection timing retard).
The prestroke controller for a fuel injection pump taught by the aforesaid Japanese Patent Disclosure No. Hei 3-233144 will be briefly explained with reference to FIG. 1.
FIG. 1 is a perspective view of the fuel injection pump prestroke controller, designated by reference numeral 1, and a conventional mechanical governor, designated reference numeral 2. On the side of the main pump unit 3 are shown a plunger 4, a control sleeve 5, and a timing control rod 6 whose engagement pin 8 is engaged with an engagement groove 7 of the control sleeve 5.
On the side of the mechanical governor 2, a cam shaft 9 for reciprocating the plunger 4 in the main pump unit 3 is fitted with a guide sleeve 10 and a flyweight 11 is connected with the guide sleeve 10.
The fuel injection pump prestroke controller 1, which comprises the flyweight 11 as a component utilized in common with the mechanical governor 2, further has a tension lever 13 serving as a prestroke control lever which pivots around a stationary pivot shaft 12 in accordance with the movement of the flyweight 11, a timing cam 14, a counterweight 15 connected with the timing control rod 6, and a cam surface abutment piece 16 formed integrally with the counterweight 15.
The timing cam 14 is connected with one side of the free end of the tension lever 13 through a connection lever 17 and is rotatable around a stationary pivot shaft 18. A cam surface abutment projection 16A of the cam surface abutment piece 16 is pressed onto the cam surface 14A of the timing cam 14 at a prescribed pressure by the force of a counterweight spring 19 (return spring).
The other side of the free end of the tension lever 13 is connected with a torque cam 21 which is part of a governor mechanism 20 of the mechanical governor 2. Although this is for enabling the governor mechanism 20 to automatically control the fuel injection quantity in response to variation in engine load, the governor mechanism 20 will not be described in detail here.
An injection quantity control rack 22 is provided in association with the torque cam 21. The injection quantity control rack 22 controls the fuel injection quantity by rotating the plunger 4 about its own axis.
In the fuel injection pump prestroke controller 1 of the aforesaid configuration, an increase in engine speed (pump speed) increases the centrifugal force of the flyweight 11 causing it to shift and slide the guide sleeve 10 along the cam shaft 9 to the right in FIG. 1. As a result, the tension lever 13 rotates about the stationary pivot shaft 12, whereby the mechanical governor 2 performs the prescribed governor function and the timing cam 14 is rotated about the stationary pivot shaft 18 by the connection lever 17.
Since this rotation of the timing cam 14 changes the positional relationship between the timing control cam surface 14A and the cam surface abutment projection 16A of the cam surface abutment piece 16, the cam surface abutment piece 16 and the counterweight 15 are rotated about the axis of the timing control rod 6.
The resulting rotation of the timing control rod 6 by a corresponding angle moves the control sleeve 5 vertically and changes the positional relationship between the control sleeve 5 and the plunger 4, thus changing the fuel injection timing or the prestroke.
Thus, as explained in the foregoing, the prestroke controller 1 controls the start of pressurized fuel delivery by the main pump unit 3 by varying the vertical positional relationship between the control sleeve 5 and the plunger 4, and the operation of the timing control rod 6 for varying the position of the control sleeve 5 relies on the use of the flyweight 11 and the tension lever 13 in common with the governor mechanism 20.
Since the flyweight 11 utilized by the prior art prestroke controller 1 moves with increasing engine speed, the prestroke controller 1 is capable of providing the injection timing advance characteristic required of a speed timer for varying the injection timing as a function of engine speed. The prior art prestroke controller 1 thus has the drawback of being all but impossible to apply for controlling prestroke in accordance with an injection timing advance characteristic during operation in a cold external environment or in response to changes in the amount of accelerator depression or the engine load state.
An object of the first aspect of the invention is to overcome the aforesaid problems of the prior art technology by providing a fuel injection pump capable of efficiently transferring the rotational force of the displacement transfer section of a governor to the timing control rod of the main pump unit without use of an oil seal or the like.
An object of the second aspect of the invention is to provide a fuel injection pump prestroke controller which employs a magnetic coupling and, by utilizing the fact that the secondary side of the magnetic coupling (driven side internal magnet) can be controlled to a desired position without relying on the driving force of the flyweight on the primary side (driving side external magnet), imparts speed timer capability to the prestroke controller, thereby increasing the degree of freedom of its injection timing advance characteristic and enabling it to conduct injection timing advance in response to temperature and load.
Still another object of the invention is to provide a fuel injection pump prestroke controller capable of conducting low-temperature injection timing advance and low-load injection timing advance independently of engine speed, i.e., of flyweight lift.